1. Technical Field
The invention relates to pneumatic tires and in particular to pneumatic tires having tie bars extending between adjacent tread blocks which are provided with an undercut configuration.
2. Background Information
Pneumatic tires such as used for passenger vehicles and trucks, have a tread pattern which extends circumferentially about the tire. The tread consists of a plurality of circumferentially and laterally extending grooves which divide the tread into generally circumferentially extending ribs formed by a plurality of either continuous or discontinuous tread blocks. The tread blocks may be separated by lateral grooves or slots which provide for expelling water to prevent hydroplaning and provide better traction in snow and mud. However, these slots and/or grooves provide increased flexibility to the tread blocks which, for certain applications, is less desirable than stiffer tread blocks. Therefore, to increase the stiffness of the tread blocks, tie bars are formed integrally with the tread blocks and extend across the grooves and slots between adjacent tread blocks. These tie bars are molded into the tire tread and have a height usually less than the depth of the tread blocks so that a top surface of the tie bar is below the surface of the tread block and only comes into contact with the road as the tire wears. These tie bars increase the stiffness of the tread blocks which is desirable for many applications and assist in maintaining this stiffness as the tread wears to a lower depth. Thus, depending upon the location of the tie bar, it may provide noise reduction, wear reduction, decreased rolling resistance, and provide increased handling and traction for the tire.
Various tie bar constructions have been developed and utilized in many tire constructions. One example shown in U.S. Pat. No. 5,022,448 shows a tie bar which is a bridge member extending between opposed grooves. In addition, other tire constructions are provided with tapered tie bars such as shown in U.S. Pat. Nos. 2,701,598; 3,727,661; 4,515,197 and 5,439,040. However, all of these tie bars are tapered outwardly from the top surface of the tie bar to enable the tie bar to increase in width as the tread wears to assist in maintaining stiffness to the adjacent lug blocks.
The present invention provides a pneumatic tire having a plurality of tie bars extending between adjacent tread blocks which are provided with undercuts to increase wet traction of the tire as the tire wears by increasing the void areas in the grooves to assist in dispersion of water.
The undercut tie bars of the invention furthermore assist in lowering tread block stiffness when compared to non-undercut tie bars. This counteracts the natural tendency for tread blocks to stiffen as the tire wears and maintains a greater similarity in performance to that of a new tire.
Another aspect of the invention is for certain tread blocks and arrangements thereof to decrease rolling resistance.
Still another feature of the invention is the ability to provide the tie bar with various undercut configurations in order to achieve various results depending upon the particular tire and tread block construction thereof.
Another feature of the invention is to provide an undercut tie bar having one or more right-angled steps forming the undercut or providing the undercut with various sloped surfaces on one or both sides of the tie bar.
A further feature of the invention is to provide a pneumatic tire having undercut tie bars in which the tie bars are molded integrally with the tread blocks of the tire without requiring major changes in the molding process or materially increasing the costs of the tire.
Another aspect of the undercut tie bars is the ability to form the undercut facing either the outside or inside of the tire or on both sides of the tie bar, depending upon the characteristics desired to be achieved.
The foregoing advantages, construction and operation of the present invention will become more readily apparent from the following description and accompanying drawings.